China's air quality is rarely something to write home about, but it was particularly nasty this week in the eastern part of the country that includes the city of Shanghai. The city of 14 million residents has essentially disappeared.

Reuters reports that since Wednesday, hazardous air pollution has forced schools to close, canceled outdoor activities and sparked complaints from residents about yellow skies and foul smells. Besides the general nastiness of the air, it's also a major health issue for people in Shanghai and other cities like Qingdao.

The city saw levels of PM2.5, or particulate matter with a diameter of 2.5 micrometers, reach a reading of 354 on Wednesday, said Nanjing-based news portal news.longhoo.net.

Levels above 300 are considered hazardous, while the World Health Organization recommends a daily level of no more than 20.

Residents... took to China's popular Twitter-like Weibo site to describe desolate streets and the apocalyptic environment. "The sky is pale yellow and the air is full of a choking smell," one user wrote.